On 1/29/07, Keith Goodman <[EMAIL PROTECTED]> wrote: > On 1/29/07, Keith Goodman <[EMAIL PROTECTED]> wrote: > > On 1/29/07, Keith Goodman <[EMAIL PROTECTED]> wrote: > > > On 1/29/07, Charles R Harris <[EMAIL PROTECTED]> wrote: > > > > > > > That's odd, the LSB bit of the double precision mantissa is only about > > > > 2.2e-16, so you can't *get* differences as small as 8.4e-22 without > > > > about > > > > 70 bit mantissa's. Hmmm, and extended double precision only has 63 bit > > > > mantissa's. Are you sure you are computing the error correctly? > > > > > > That is odd. > > > > > > 8.4e-22 is just the output of the test script: abs(z - z0).max(). That > > > abs is from python. > > > > By playing around with x and y I can get all sorts of values for abs(z > > - z0).max(). I can get down to the e-23 range and to 2.2e-16. I've > > also seen e-18 and e-22. > > Here is a setting for x and y that gives me a difference (using the > unit test in this thread) of 4.54747e-13! That is huge---and a serious > problem. I am sure I can get bigger. > > # x data > x = M.zeros((3,3)) > x[0,0] = 9.0030140479499 > x[0,1] = 9.0026474226671 > x[0,2] = -9.0011270502873 > x[1,0] = 9.0228605377994 > x[1,1] = 9.0033715311274 > x[1,2] = -9.0082367491299 > x[2,0] = 9.0044783987583 > x[2,1] = 0.0027488028057 > x[2,2] = -9.0036113393360 > > # y data > y = M.zeros((3,1)) > y[0,0] =10.00088539878978 > y[1,0] = 0.00667193234012 > y[2,0] = 0.00032472712345
OK. I guess I should be looking at the fractional difference instead of the absolute difference. The fractional difference is of order e-16. _______________________________________________ Numpy-discussion mailing list [email protected] http://projects.scipy.org/mailman/listinfo/numpy-discussion
